Nepetalactone → Puleganic acid

Participants

Reaction Conditions

Reaction Steps

This example shows the effect of treating crude catmint oil by steam distillation, followed by distillation with isopropanol on the rate of hydrogenation of nepetalactone (NPL) to DHN. Catmint oil (2400 grams; Lot 2003 from George Thacker Sons) and deionized water (1440 grams) were combined in a 4 liter heated resin kettle outfitted with a shell and tube condenser and a dry ice cold finger. This resin kettle was outfitted with a vacuum control. Vacuum was controlled at a pressure of 6.9 kPa while the kettle was heated using an electrical heating mantel. The temperature of the water and catmint oil was controlled at 39 to 45° C. Water and some of the catmint oil was stripped off, condensed using the shell and tube condenser and the cold finger and periodically drained from the condenser receiver. After about 7 hours, most of the water was distilled off and a total of approximately 400 mL of isopropanol was added to the catmint oil remaining in the resin kettle. The distillation was continued at about 6.9 kPa but the temperature of the catmint oil/isopropanol mixture was raised to 72 to 80° C. to facilitate the distillation. The distillation was carried out for an additional hour. For the last 10 to 15 minutes, the vacuum was adjusted to 752 Pa to help drive off any residual isopropanol. About 4.5 wt % of the initial charge of the oil was distilled off in this fashion. A total of 7 distillations were performed in this fashion and the distilled catmint oil obtained from the distillations was combined to give a total of about 14.7 Kg of distilled catmint oil. A small portion was used in a hydrogenation test performed as described in Comparative Example 1. Table 4 shows the rate of hydrogenating this treated oil as the NPL conversion as a function of hydrogenation time or time on stream (TOS). After 1.75 hours of hydrogenation, the conversion of the nepetalactone was 82.2%, which is substantially higher than the conversion at approximately the same time in Example 1. This was done with no apparent increase in nepetalic acid or yield loss to puleganic acid. The crude catmint oil had an initial sulfur content of 278 ppm; the content of the sulfur in the sample used for hydrogenation was 205 ppm.

Provenance & Evidence